The Patent Application relates to a process for the production of a MIS (metal-insulator-substrate) field effect transistor having an adjustable, extremely short channel length. An insulating layer is applied to the surface of a semiconductor substrate and a gate electrode layer is applied to this insulating layer. Ion implantation is used to produce in the semiconductor substrate a drain and a source zone of the first conductivity type and a second doped zone of the second conductivity type which surrounds the source zone at least in the direction of the drain zone, and which at the side of the source zone adjoins the substrate surface. The channel zone consists of the intermediate zone of the semiconductor substrate which lies between the outer edge of the second doped zone which adjoins the substrate surface and the adjacent edge of the source zone.
The reduction in size of the structure of MOS devices unintentionally entails an impairment of the electrical properties of the elements, which is manifest, for example, in a shift of the threshold voltage, the punch-through of the drain voltage, and possibly also an increase of the body effect.
The reduction in structure size also results in a greater influence of the tolerances in the geometric structure production and transfer. A reduction in tolerances can only be achieved with increased apparatus expense. In order to avoid this, alternative self-adjusting processes must be found.
A process of the type described in the introduction is disclosed in the German OS No. 27 03 877 corresponding to U.S. application Ser. No. 870,216 now U.S. Pat. No. 4,190,850 (DIMOS transistor), incorporated herein by reference, in which the effective channel length is adjusted by bevelling the edge of the gate electrode which is composed of polycrystalline silicon. The wedge-shaped path of the gate electrode layer over the channel zone facilitates a "self-adjusting" production of the source zone and of the second doped zone by which it is surrounded, since the gate electrode layer is used as an implantation mask. The energy used for the implantation of the second doped zone is such that, in accordance with the increase in thickness of the gate electrode layer the implanted ions penetrate less deeply into the semiconductor substrate, and in this way the concentration maximum of the ions implanted to form the second doped zone passes through the surface of the semiconductor substrate at a short distance from the edge of the source zone. The distance between this through line and the edge of the source zone can be determined via the magnitude of the wedge angle. This distance constitutes the length of the channel used for the MIS field effect transistor. Increasing reduction in the geometry of the components means that high demands must be made on the reproducibility of the mask edge and on the homogeneity of the gate material. Furthermore it is difficult to use this (DIMOS) process in combination with metal gates.